MICROSTRUCTURAL ANALYSIS OF POLY[(L,L-LACTIDE)-CO-(GLYCOLIDE)] BY H-1AND C-13 NMR-SPECTROSCOPY

The C-13 nuclear magnetic resonance (n.m.r.) spectra were found to pro vide a means for direct observation of the structures formed along the glycolide/lactide copolymer chain upon transesterification. Neverthel ess H-1 n.m.r. spectroscopy appeared to be more convenient and useful in the analysis of chain microstructure. The glycolide methylene group region of the proton spectra exhibits several signals which can be as cribed to longer sequences (as compared to those giving rise to C-13 r esonances) as well as to the sequences which can appear only as a resu lt of the second mode of transesterification. The analysis revealed th at the longest blocks were in the copolymers prepared with Al(acac)(3) as the initiator and the shortest blocks were in the copolymers obtai ned with tin initiators. A decrease in temperature was found to reduce the extent of the second mode of transesterification.